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Saliby et al., Houston, TX, followed 157 patients retrospectively with
regard to the question if re- testing for adequacy of thyroid hormone substitution
has been sufficient in these patients. After exclusion of patients for
reasons of non-compliance, effects of drugs, or other conditions, 71 patients
remained for analysis. The range of follow-up varied between 6 months and
4 years. It appeared that 11.6% of patients required a change in the dose
at 4 months, 25% at 6 months, 31.2% at 9 months, and 52% at 12 months of
follow-up. Overall 79% required a dose change at 42 months. From this and
other data it was concluded that hypothyroid patients, receiving LT4 replacement,
required more frequent re-testing than previously recommended, for instance
every 4-6 months.
Iervasi et al., Pisa, Italy, and Los Angeles, CA, serially measured thyroid function in 24 patients with cardiac arrhythmias who were treated with amiodarone: 20 mg/kg/day i.v. on day 1, 10 mg/kg/day i.v. on day 2, 600 mg/day orally 7-10 days, and then gradually reduced to 400- 200 mg/day orally. Total and free T4 concentration increased significantly from the fourth day of therapy, while FT3 and TT3 decreased from the second day (only TT3 significantly). TSH increased from the first day progressively, followed by a parallel increase of TT4/TT3 ratio (r = 0.980). Reverse T3 significantly increased from day 2 and paralleled TSH values. It is concluded that during treatment with amiodarone TSH changes first, followed by rT3, T4, and T3. The authors also state that the increase in total and free T4 reflect at least in part contribution of direct thyroidal stimulation by TSH and further that the progressive fall of TT3 reflects inhibition of peripheral conversion of T4 to T3. (Comment: The fact that TSH is the first to change, suggests an effect of amiodarone at the pituitary level. An additional explanation for the increase of T4 parameters may be inhibition of T4 clearance due to blockade of T4 transport into tissues and/or T4 to T3 conversion by amiodarone. The fact that in contrast to the decrease in TT3, FT3 does not significantly decrease, suggests rather an increased serum binding of T3 than a decreased T3 production.) |
